This paper develops a framework to measure the exposure to systematic risk for pools of asset securitizations and measures empirically whether current ratings- based rules for regulatory capital of securitizations under Basel II and Basel III re ect this exposure. The analysis is based on a comprehensive US dataset on asset securitizations for the time period between 2000 and 2008. We nd that the short- fall of regulatory capital during the Global Financial Crisis is strongly related to ratings. In particular, we empirically show that insucient capital is allocated to tranches with the highest rating. These tranches account for the greatest part of the total issuance volumes. Furthermore, this paper is the rst to calibrate risk weights which account for systematic risk and provide sucient capital buers to cover the exposure during similar economic downturns. These policy-relevant ndings suggest a re-calibration of RBA risk weights and may contribute to the current eorts by the Basel Committee on Banking Supervision and others to re-establish sustainable securitization markets and to improve the stability of the nancial system.